Origin of hexavalent chromium in groundwater: The example of Sarigkiol Basin, Northern Greece.

Hexavalent chromium constitutes a serious deterioration factor for the groundwater quality of several regions around the world. High concentrations of this contaminant have been also reported in the groundwater of the Sarigkiol hydrological basin (near Kozani city, NW Greece). Specific interest was paid to this particular study area due to the co-existence here of two important factors both expected to contribute to Cr(VI) presence and groundwater pollution; namely the area's exposed ophiolitic rocks and its substantial fly ash deposits originating from the local lignite burning power plant. Accordingly, detailed geochemical, mineralogical, hydro-chemical, geophysical and hydrogeological studies were performed on the rocks, soils, sediments and water resources of this basin. Cr(VI) concentrations varied in the different aquifers, with the highest concentration (up to 120µgL-1) recorded in the groundwater of the unconfined porous aquifer situated near the temporary fly ash disposal site. Recharge of the porous aquifer is related mainly to precipitation infiltration and occasional surface run-off. Nevertheless, a hydraulic connection between the porous and neighboring karst aquifers could not be delineated. Therefore, the presence of Cr(VI) in the groundwater of this area is thought to originate from both the ophiolitic rock weathering products in the soils, and the local leaching of Cr(VI) from the diffused fly ash located in the area surrounding the lignite power plant. This conclusion was corroborated by factor analysis, and the strongly positively fractionated Cr isotopes (δ53Cr up to 0.83‰) recorded in groundwater, an ash leachate, and the bulk fly ash. An anthropogenic source of Cr(VI) that possibly influences groundwater quality is especially apparent in the eastern part of the Sarigkiol basin.

Regional cerebral blood flow and cellular environment in subarachnoid hemorrhage: A thermal doppler flowmetry and microdialysis study.

BACKGROUND: Cerebral microdialysis enables assessment of regional metabolic physiology and provides biomarkers for clinical correlation in critical conditions, such as subarachnoid hemorrhage (SAH). The aim of our current study was to investigate the correlation between regional cerebral blood flow and microdialysis parameters (glucose, lactate, glycerol, pyruvate concentrations, and lactate/pyruvate metabolic ratio) in patients with SAH. MATERIALS AND METHODS: Twenty-one patients with SAH were enrolled in our retrospective study. Cerebral blood flow (CBF) based on thermal diffusion methodology, the thermal coefficient K, and microdialysis biochemical markers were recorded. The duration of the brain monitoring was 10 days. RESULTS: Microdialysis glucose concentration was inversely related to the cerebral temperature and to the L/P ratio. Furthermore, it was positively correlated to all other microdialysis parameters but glycerol. The K coefficient was strongly and positively correlated with the temperature and marginally with the CBF. The L/P ratio was positively correlated with glycerol, while it was inversely correlated with the CBF. Patients who died had elevated L/P ratio and K coefficient compared to the survivors in our series. CONCLUSIONS: Thermal conductivity coefficient may change over time as cerebral injury progresses and tissue properties alter. These alterations were found to be associated with the microdialysis metabolite concentrations and the CBF itself. The microdialysis biochemical indices of cell stress and death (glycerol, L/P ratio) were positively related to each other, while the measured L/P metabolic ratio was higher among patients who died.

Hydrocephalus and aquaporins: the role of aquaporin-4.

INTRODUCTION: Aquaporins (AQPs) are membrane proteins that facilitate water and small solute movement in tissues. Hydrocephalus is the major central nervous system disorder associated with defective cerebrospinal fluid turnover. Aquaporin-4 (AQP4) is a water channel located mainly at the blood-brain barrier (BBB) and blood-cerebrospinal fluid (CSF) interfaces and is associated with the elimination of cerebral edema via these routes. The aim of this study is to review the pertinent literature concerning the role of AQP4 in the pathophysiology of hydrocephalus. METHODS: We performed a MEDLINE search using the terms aquaporin AND hydrocephalus. The results of the search were further refined to exclude studies not related to aquaporin-4. RESULTS: Six studies were identified. All studies utilized an animal model such as AQP4-knockout mice, H-Tx rats, and kaolin and L-α-lysophosphatidylcholine (LPC) stearoyl injection models of hydrocephalus. Most studies indicate that there is an up-regulation of AQP4 expression at the BBB and blood-CSF interfaces in cases of hydrocephalus. One study, reported sporadic cases of obstructive hydrocephalus in a subgroup of AQP4-knockout mice. CONCLUSIONS: Few publications have studied the association between aquaporins and hydrocephalus. Currently, all the existing studies rely on animal models. An adaptive and protective role of AQP4 to increase the resolution of the "hydrocephalic" edema at the BBB and blood-CSF interfaces is proposed in the pathophysiology of hydrocephalus. Further research is needed to clarify if this association exists in humans.

Hydrocephalus and aquaporins: the role of aquaporin-1.

INTRODUCTION: Aquaporins (AQPs) are membrane proteins that facilitate water and small solute movement in tissues. Hydrocephalus is a major central nervous system disorder associated with defective cerebrospinal fluid (CSF) turnover. Aquaporin-1 (AQP1) is a water channel located mainly at the choroid plexus epithelium and plays an active role in CSF production. The aim of this study is to review the pertinent literature concerning the role of aquaporin-1 in the pathophysiology of hydrocephalus. METHODS: We performed a MEDLINE search using the terms aquaporin AND hydrocephalus. The results of the search were further refined to exclude studies not related to aquaporin-1. RESULTS: Five studies were identified. Three of these studies utilized an animal model, while only two studies referred to a few human cases of hydrocephalus. Most of the studies indicate that there is a down-regulation of AQP1 expression in choroid plexus in models of hydrocephalus. A small series of human choroid plexus tumors showed that AQP1 expression is up-regulated. In cases of human choroid plexus tumors, there are indications that AQP1 may have alternative physiologic roles, but it is not clear whether this is associated with a specific type of hydrocephalus or the genetic burden of the tumor. CONCLUSION: There has been a paucity of research on the link between aquaporins and hydrocephalus. Most studies have relied on animal models. An adaptive and protective role of AQP1 as a regulator of CSF production is proposed in the pathophysiology of hydrocephalus. Further research is needed to clarify if this association exists in humans.

Extra-framework cation release from heulandite-type rich tuffs on exchange with NH(4)(+).

The outgoing cations of Greek heulandite-rich tuff samples (heulandite type-III, 91wt.%, mica 4wt.%, feldspar 5wt. %, CEC 2.22meq/g) were analysed upon exchange with ammonium acetate using atomic absorption spectrometry (AAS). The kinetic curves of each cation were investigated over a total time of contact of 720h with sampling at frequent intervals. The materials were examined by powder X-ray diffraction, SEM-EDS, and AAS. The sorption ability was measured using the ammonium acetate saturation method. It was found that Ca(2+) presents an unexpected extra-framework release and a surprisingly high degree of exchange (90%). The exchange of Mg (57%) is also worthy of note whereas the behavior of K(+) showed an expected rapid initial release. The behavior of Na(+) must be similar. However, its lower concentration in the zeolitic material minimizes its overall significance somewhat. On the other hand, Ca(2+) and Mg(2+) release is kinetically much slower, compared to that of alkali metal ions, and this phenomenon indicates that different exchange energies are needed till final equilibrium.

Insertion of long-term tunneled cuffed hemodialysis catheters via the external jugular vein by using a simple, safe and reliable surgical technique.

OBJECTIVE: Description of our technique for the insertion of long-term tunneled cuffed hemodialysis (HD) catheters via the external jugular vein. METHODS: From December 1999 to August 2006, 357 long-term tunneled cuffed HD catheters were inserted in 308 patients, who were referred to us from various hospitals and clinics in Greece. About half of them (168, or 47%) were inserted via the external jugular vein. We describe our surgical technique for the insertion of long-term tunneled cuffed HD catheters via the external jugular vein. RESULTS: During our study, there was a gradual increase in using the external jugular vein as a method for the insertion of permanent HD catheters. In all cases, the intraoperative catheter blood flow was measured >300 ml/min. No major complications occurred. CONCLUSIONS: Long-term tunneled cuffed HD catheters can be inserted via the external jugular vein by using an easy, simple, safe surgical technique. This procedure provides the possibility of using the internal jugular vein in the future.

Investigation of the uptake ability of fly ashes produced after lignite combustion.

Fly ash samples from the five steam electric power stations of the Lignite Center of Western Macedonia were used in this study. They consisted mainly of anhydrite, lime, quartz and amorphous material as well as feldspars, calcite, micas + clays, portlandite and gehlenite which were all present in minor amounts. Anhydrite, lime and portlandite in the fly ash samples diminished upon treatment with ammonium acetate aqueous solution, whereas quartz, feldspars, gehlenite and amorphous material were enriched. The uptake ability of the fly ash samples ranged from 89 to 101 mequ./100g. The uptake ability of the samples was mainly attributed to the amorphous material and the microporous minerals, micas + clays. The amorphous material content was estimated at between 17 and 20 wt% in the treated fly ashes and may be unburned organic matter and amorphous inorganic material that resulted during the combustion of the lignite. A positive correlation was observed between the uptake ability and the total percentage of amorphous material and micas + clays. The relatively high uptake ability of the fly ash samples could lead to additional industrial and environmental uses of the fly ashes. The environmental advantage of fly ash exploitation will be particularly important for large electric power centers, such as the LCWM.

Characterisation of zeolitic materials with a HEU-type structure modified by transition metal elements: definition of acid sites in nickel-loaded crystals in the light of experimental and quantum-chemical results.

Nickel-loaded HEU-type zeolite crystals have been obtained by well-known synthetic procedures and characterised by X-ray fluorescence (XRF), scanning-electron microscopy/ energy-dispersive spectroscopy (SEM-EDS), FT-IR, diffuse reflectance UV/ Vis spectroscopy (DR(UV/Vis)S) and X-ray photoelectron spectroscopy (XPS) measurements as non-homoionic and non-stoichiometric substances containing exchangeable hydrated Ni2+ ions in the micropores and nickel hydroxide phases supported on the surface. Thermogravimetric analysis/differential gravimetry (TGA/DTG) and differential thermal analysis (DTA) demonstrated that full dehydration below approximately 400 degrees C follows a clearly endothermic process, whereas at higher temperatures the zeolite is amorphised and finally partially recrystallised to Ni(Al,Si) oxides, detected by powder X-ray powder diffraction (XRD). The solid acidity of NiHEU, initially determined by temperature-programmed desorption (TPD) of ammonia to be 8.93 mgg(-1) NH3, is attributed to the weak acid sites (fundamentally Lewis sites) resolved at approximately 183 degrees C, and to the strong acid sites (essentially Brønsted sites) resolved at approximately 461 degrees C in the TPD pattern. A more sophisticated study based on in situ/ex situ FT-IR with in situ/ex situ 27Al MAS NMR and pyridine (Py) as a probe molecule, revealed that the Lewis acid sites can be attributed primarily to Ni2+ ions, whereas the Brønsted ones can probably be associated with the surface-supported nickel hydroxide phases. The spectroscopic measurements in conjunction with powder XRD and 29Si MAS NMR data strongly suggest that distorted Al tetrahedra are formed during the dehydration process and Py chemisorption/complexation (NiHEU-Py), whereas the crystal structure is remarkably well preserved in the rehydrated material (NiHEU-Py/R). The structural, electronic, energetic and spectroscopic properties of all possible nickel(II) aqua and dihydroxy complexes absorbed in the zeolite micropores or supported on the zeolite surface were studied theoretically by density functional theory (DFT). The computed proton affinity, found to be in the range 182.0-210.0 kcalmol(-1), increases with increasing coordination number of the aqua and dihydroxy nickel(II) complexes.

Degree of familiarity ART2 in knowledge-based landmine detection.

The self-organizing network ART2 is extended to provide a fuzzy output value, which indicates the degree of familiarity of a new analog input pattern to previously stored patterns in the long-term memory of the network. The outputs of the multilayer perceptron and this modified ART2 provide an analog value to a fuzzy rule-based fusion technique which also uses a processed polarization resolved image as its third input. In real-time situations these two classifier outputs indicate the likelihood of a surface landmine target when presented with a number of multispectral and textural bands. Due to the modifications in ART2 this updated alternative architecture (to that of a previous network in [3]) has improved real-time landmine detection capabilities although the registration of all bands is more critical to the accuracy of results in this case. The real-time fuzzy rule-based system in preliminary tests has detected two of the three landmines and the landmine surrogate with two false alarms. Advanced tests on 30 images using the fuzzy rule-based system further confirmed the distinct advantages of fusion and improved detection rates.